A kelly hose (also known as a mud hose or rotary hose) is a flexible, steel reinforced, high pressure hose that connects the standpipe to the kelly (or more specifically to the goose-neck on the swivel above the kelly) and allows free vertical movement of the kelly while facilitating the flow of drilling fluid through the system and down the drill string.[1] The Kelly hose has a diameter of 3-5 inches (inside diameter).[2]